Interference fringes were produced using light in a doulbe-slit experiment. When a mica sheet of uniform thickness and refractive index 1.6 (relative to air) is placed in the path of light from one of the slits, the central fringe moves through some distance. This distance is equal to the width of 30 interference bands if light of wavelength 4800 is used. The thickness (in `mu m`) of mica is

Options

A. 90
B. 12
C. 14
D. 24

Answer

D

Explanation

Shift of fringe pattern
`:. (30 D(4800 xx 10^(-10)))/(d) = (0.6) t (D)/(d)`
`30 xx 4800 xx 10^(-10) = 0.6`
`t = (30 xx 4800 xx 10^(-10))/(0.6) = (1.44 xx 10^(-5))/(0.6)`
`= 24 xx 10^(-6)`